How to use interface template? How to model interface template properly in D.

[Jacob Carlborg]

On 2011-05-27 07:55, Matthew Ong wrote:
> Hi All,
>
> The main aim here is to find out how to model similar syntax within D.
>
> Due to the nature of the architecture of the library that I have
> designed in Java and heavily leans towards interface generics.
> It works well with java.
>
> Yes. I am aware about Tuple to allow me to do multiple value return.
> The point is Not about returning multiple, but how to moduel
>
> public interface DefType1<T1> { // Please note this is like interface
> template
> public Throwable getError();
> public T1 getValue();
> public String getDesc();
> }
> // Elsewhere.
>
> public class RetVal1<T1> implements DefType1<T1> {
>
> private RetVal1() {
> }
>
> public static <T1> RetVal1<T1> make(T1 value) {
> RetVal1<T1> obj = new RetVal1<T1>();
> obj.mValue = value;
> return obj;
> }
>
> private Throwable mError;
>
> public void setError(Throwable error) {
> mError = error;
> }
>
> public Throwable getError() {
> return mError;
> }
> private T1 mValue;
>
> public T1 getValue() {
> return mValue;
> }
> private String mDesc;
>
> public String getDesc() {
> return mDesc;
> }
> }
>
> // Yet, else where
> class Account{...}
>
> public static RetVal1<Account> methodA(int num, String str) { // similar
> to Instantiation template
> ... // do something.
> return RetVal2.<Account>make(num, str);
> }
>
> void main(string[] args){
> RetVal1<Account> ret = methodA(1, "abc"); // some method call that return
> if(ret.getError()==null){
> Account acc=ret.getValue1();
> prnln("amount=" + acc.getAmount());
> }
> }
> http://www.digitalmars.com/d/2.0/template.html#Constraint
> Struct, Union, and Interface Templates
> ...
> Analogously to class templates, struct, union and interfaces can be
> transformed into templates by supplying a template parameter list.
> However there is no example shown.
> In D the syntax should more or less look similar:
>
> interface DefType1(T1) { // No issue here
> public:
> Throwable getError();
> T1 getValue();
> String getDesc();
> }
>
> public class RetVal1(T1) : DefType1(T1) { // ### or IS IT: DefType1!(T1) ??
> ...
> public static RetVal1(T1) make(T1)(T1 value) { // static method template
> RetVal1(T1) obj = new RetVal1(T1)(); // ### or IS IT: new RetVal1!(T1)();
> obj.mValue = value;
> return obj;
> }
> ...
> }
>
>
> public static RetVal1(Account) methodA(int num, String str) { //### How
> to do that?? Compilation error.
> Account acc=new Account();
> ... // do something.
> return RetVal2.(Account)make(ac); //### How to do that?? compilation
> error also
> }
>
> RetVal1(Account) ret = methodA(1, "abc"); // Compilation error also.
> if(ret.getError()==null){
> Account acc=ret.getValue1();
> prnln("amount=" + acc.getAmount());
> }
> ------------------------------------------------------------------------
> Kindly show some compilable and working code sample.
>
> Thanks very much.
>

In D the syntax for declaring a template and instantiate a template is 
not the same. Have a look at the first example of 
http://www.digitalmars.com/d/2.0/template.htm
If don't understand after reading that example please ask again, I don't 
want to just give away the answer. You'll learn more by reading the 
documentation and figuring it out by yourself.

-- 
/Jacob Carlborg